A known parking assist device disclosed in JP59-201082A assists a vehicle to be parked into a parking stall as follows. First, the known parking assist device detects an actual steering angle by means of a steering sensor, and then, on the basis of a detected vehicle position and a predetermined data, which relates to a parking operation and previously inputted into the parking assist device. Then, the parking assist device calculates a required steering angle, which is required for the parking operation and displaying the required steering angle, is calculated, and further, and finally the parking assist device displays an instructing angle, which is required for operating the steering in order to park the vehicle into the parking stall, on a simple display means. Because the parking assist device disclosed in JP59-201082A calculates the steering angle on the basis of only the steering sensor, an error on detecting relative positions between the vehicle and the parking stall has been occurred. In consideration of such errors, parking assist devices disclosed in JP6-111198A, JP11-208420A, JP2000-079860A and JP2003-205807A, detect a parking target position after processing a rear image that is captured by, for example a CCD camera (charge-coupled device camera).
Specifically, the parking assist device disclosed in JP6-111198A captures a predetermined area around the vehicle including a parking stall by means of the CCD camera, calculates distances from the vehicle to the parking stall in each azimuth, and selects a single distance which is shortest, and set it as an entrance of the parking stall. Specifically, the parking assist device disclosed in JP11-208420A superposes an image that indicating a temporary parking target position of the vehicle on the captured image and sets a parking target position by adjusting the temporary parking target position by a position adjusting means such as a touch panel. More specifically, the parking assist device disclosed in JP2000-079860A sets a specific area of window in the vicinity of a white line and recognizes a parking stall depending on feature and the geometrical arrangement of the white line. Furthermore, in the light of a driving characteristic of a driver who generally passes in front of a parking target position and then turns the vehicle in order to park the vehicle into the target position, the parking assist device disclosed in JP2003-205807A assumes a parking target position on the basis of a running state of the vehicle before the parking operation and a moving locus and sets an initial displaying position within an adjusting frame for setting a target of the parking.
However, because the known parking assist device disclosed in JP6-111198A uses the image captured by the camera without applying any process, the parking target position cannot be detected accurately due to external elements such as a parking stall line of another parking stall, an image of another vehicle, which can be an obstacle, and a shadow of a building. In such case, it may be considered that an accurate parking target position can be obtained by executing the calculating operation over and over again, however, such measure is not general for the image data processing operation. The known parking assist device disclosed in JP2000-079860A processes within a certain area of the captured image, which is regulated by the window, in order to detect the parking stall line, so that another vehicle that may be an obstacle or element such as a background image, which may result in disturbance (brightness, a shadow of the vehicle and dirt on a road surface), can be eliminated. However, because the known parking assist device disclosed in JP2000-079860A needs to move the vehicle until the guide line reaches the target parking stall, the user need to do an extra operation. Thus, the level of easiness to park the vehicle by means of the parking assist device, which can rotates the wheel automatically, has been reduced.
Further, according to the known parking assist device disclosed in JP11-208420A, the driver need to adjust the temporary parking target position in order to set the parking target position correctly, as a result, the driver also need to do an extra operation, for example moving the temporary parking target position in a vertical direction and in a horizontal direction for each 2 dots, and setting the angle of the parking target position.
Furthermore, according to the known parking assist device disclosed in JP2003-205807A, because the vehicle moving locus may differs depending on levels of driving techniques or situations of the parking stall, for example, a position of another vehicle, which is parked in the vicinity of the target parking stall, it can be determined that the driver intends to park the vehicle into one of the left and the right parking stalls, however, the parking target position may be out of the parking stall. Thus, the driver need to adjust the adjusting frame displayed on the display by position adjusting means such as a touch panel in order to readjust the parking target position, as a result, it takes some time for the driver to set the parking target position.
A need thus exists to provide a parking assist device that can set a parking target position with high speed and high accuracy and can reduce burden on the user for setting the parking target position of the parking assist device.